Analysis and Design of Feedforward Linearity-Improved Mixer Using Inductive Source Degeneration

This paper presents a new linearity-improvement feedforward transconductance stage using inductive source-degeneration amplifiers. The proposed technique is applied to a CMOS RF mixer based on a folded-type topology. Feedforward compensation is achieved by cancelling the third-order transconductance terms between the inverter and auxiliary amplifiers. From a new theoretical analysis of the nonlinearities of the proposed circuit, the third-order intermodulation distortion is eliminated by controlling the values of the source-degeneration inductances. The proposed mixer achieves a third-order input intercept point of -5.24 dBm, which is an improvement of 6.3 dB compared with that of the conventional structure, and has the highest figure-of-merit among other linearity improved mixers that have been previously reported.